A conventional radio control interface includes a low speed 2, 3, or 4 wire configuration interface, such as a serial-peripheral interface (SPI) bus or an I2C™ bus, and one or more dedicated control pins to control the modes of operation of the radio. Such an interface may be used by a baseband chip to control a radio frequency (RF) chip.
Certain radio applications may require high bandwidth and low latency in this interface. One situation where a radio control interface may benefit from low latency is when the baseband chip performs a closed loop control operation, such as automatic gain control. In one example of a closed loop operation, the baseband chip issues a command to the RF chip. The RF chip responds to the command, causing a change in the output from the RF chip to the baseband chip. The signal is then converted to a digital signal by an analog to digital converter (ADC) on the baseband chip and used to determine the next register value to write to the RF chip. In the case of automatic gain control, the baseband chip follows this process to estimate the receive level of a signal digitally and adjust the RF chip gain over a number of iterations bring the received level to a fixed target. Minimizing the latency of the control interface when performing functions such as automatic gain control can provide significant benefits in ease of implementation and can reduce the amount of parallel logic needed to meet timing requirements.
Some radio applications, such as audio or video distribution systems, have high bandwidth requirements for transmission of large amounts of data. Such applications can also benefit from a high bandwidth and low latency interface between the baseband and the RF chips.